Regular Expressions (Regexes), what are they?

Here we look at and define regular expressions, which allow us to describe, formally, what a language is. They are defined using three "base" cases (empty string, empty set, and a single character), and three "inductive" cases (union, concatenation, and star).

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▶ADDITIONAL QUESTIONS◀
1. What other operators can be included that can be achieved from union, concatenation, and star?

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